Semiconductor technologies have created a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer superior spatial resolution compared to, e.g. photon beams because their wavelengths are shorter than the wavelengths of light beams.
Inspection devices using charged particle beams such as scanning electron microscopes (SEM) have many functions in a plurality of industrial fields, including, but not limited to, inspection of electronic circuits during manufacturing, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. In such particle beam systems fine probes with high current density can be used. For instance in case of an SEM, the primary electron (PE) beam generates particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and analyze a specimen.
Many instruments use magnetic, electrostatic or compound electrostatic-magnetic objective lenses to focus the primary beam onto the specimen. In some cases, the electrical field of the objective lens simultaneously collects the generated particles (SE and BSE), which are entering into the lens, and are guided onto a detector. For uniform and high efficiency electron collection and detection the secondary and/or backscattered particles are beneficially separated from the primary beam. With decreasing feature size in semiconductor device technology there is a need for increasing spatial resolution into the sub-nanometer range at low landing energies. In particular low landing energies below 1 keV are required to reduce scattering inside the sample which may limit spatial resolution.
For high resolution imaging devices based on electron optics systems reduced aberrations and/or an improved aberration correction is one aspect to be considered. The provision of charged particle beam devices having aberration correction is beneficial.
Prior art SEM columns are limited in their achievable resolution due to the diffraction limit, chromatic and/or spherical aberrations of the objective lens and/or other optical components included in the SEM column. In particular at low landing energies of 5 keV or below, in particular 500 eV or below, chromatic aberration is the limitation. This aspect can be addressed by providing a monochromator device adapted for reducing an energy width of the charged particle beam. Due to an enlargement of the aperture angle, however, spherical aberration prevents a significant improvement of resolution.